Determination of a phase correction is necessary when making interferometric measurements of gauge blocks with an auxiliary platen. The phase correction compensates for the differences in the reflecting properties of the gauge block and the platen surfaces. Different phase corrections are reported for gauge blocks of different manufacturers, made from different materials and with different surface roughness compared to the platen. In this paper, the process of selection of the best surface roughness parameter and the influence of different complex refractive indices of the same type of material are analysed. The new surface roughness parameter based on the difference between the weighted mean of maximum and minimum asperities of 3D surface roughness measured by a modernized Linnik phase shifting interferometer is introduced. The results of comparison of the phase correction values calculated from the difference between the weighted mean values and calculated from stack method measurements are presented and discussed. The complementary method of phase correction measurement based on the cross-wringing method with the use of the modernized phase shifting Kösters interferometer is proposed.
The results of the inter-RMO key comparison EUROMET.L-K5.2004 on the calibration of a step gauge are reported. Eighteen National Metrology Institutes and one Designated Institute from four different metrological regions all over the world participated in this comparison which lasted three years, from December 2004 to December 2007.A lack of stability was observed through the shifting of some of the inserted gauges. In order to save the comparison and get valuable and useful conclusions, it was agreed to exclude four gauges from calculation and assume that only seven gauges were reasonably stable so as to get the corresponding reference values. It was also agreed to divide the participants into two groups, analyze separately their results and, taking the pilot as the linking laboratory, refer the results to common reference values.The inverse-variance weighted mean was taken as reference value. Due to the significant instability of the step it was also considered an artefact uncertainty. The reported uncertainties ranged from 0.045 µm to 1.2 µm (k = 1). The uncertainty of the artefact ranged from 0.018 µm (for the 20 mm face) to 0.176 µm (for the 400 mm face).The compatibility of all participants for measuring step gauges was demonstrated with the only exception of a participant showing very high systematic (both positive and negative) errors. Five participants communicated higher uncertainties than the corresponding approved CMCs. A set of Recommendations and Actions were agreed therefore.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
The key comparison EURAMET.L-K1.2011 on gauge blocks was carried out in the framework of a EURAMET project starting in 2012 and ending in 2015. It involved the participation of 24 National Metrology Institutes from Europe and Egypt, respectively. 38 gauge blocks of steel and ceramic with nominal central lengths between 0.5 mm and 500 mm were circulated. The comparison was conducted in two loops with two sets of artifacts. A statistical technique for linking the reference values was applied. As a consequence the reference value of one loop is influenced by the measurements of the other loop although they did not even see the artifacts of the others. This influence comes solely from three "linking laboratories" which measure both sets of artifacts. In total there were 44 results were not fully consistent with the reference values. This represents 10% of the full set of 420 results which is a considerable high number. At least 12 of them are clearly outliers where the participants have been informed by the pilot as soon as possible. The comparison results help to support the calibration and measurement capabilities (CMCs) of the laboratories involved in the CIPM MRA. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).
This paper shows the result of work of the Institute of Micromechanics and Photonics at Warsaw University of Technology and the Length and Angle Division of Central Office of Measures (GUM) [1] in building an automatic multiwavelength interferometric system with extended measurement range for calibration of long (up to 1 m) gauge blocks. The design of a full working setup with environmental condition control and monitoring systems, as well as image analysis software, is presented. For length deviation determination the phase fraction approach is proposed and described. To confirm that the system is capable of calibrating gauge blocks with assumed accuracy, a comparison between the results of 300 mm length gauge block measurement obtained by using other systems from the Central Office of Measures is made. Statistical analysis proved that the system can be used for high precision measurements with assumed standard uncertainty (125 nm for a length of 1 m). Finally the comparison between our results obtained for a long gauge block set (600 mm to 1000 mm long) and previous calibrations made by the Physikalisch-Technische Bundesanstalt (PTB) [2] is shown.
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